Resonant Raman scattering by plasmons in n-type Ge

We have measured the Raman efficiency for plasmon scattering in n-type Ge as a function of laser excitation frequency in the range of the E₁ and E₁+Δ₁ optical gaps (2.1–2.5 eV). Our results can be explained by a mechanism involving the macroscopic electric field that accompanies the plasma oscillation in a manner similar to that responsible for Fröhlich-interaction-induced forbidden LO-phonon resonances in polar semiconductors plus some contribution of the standard cdf mechanism for scattering by plasmons.